Mendelian Genetics

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Information about Mendelian Genetics
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Published on December 11, 2007

Author: Chyou

Source: authorstream.com

Gregor Mendel And The Genetic Revolution:  Gregor Mendel And The Genetic Revolution Timothy G. Standish, Ph. D. Introduction- Gregor Mendel:  Introduction- Gregor Mendel Father of classical genetics. Born Johan Mendel in 1822 to peasant family in the Czech village of Heinzendorf part of the Austro-Hungarian empire at the time. Austrian Augustinian monk (Actually from Brunn which is now in the Czech Republic). Gregor Mendel - Work:  Gregor Mendel - Work Starting in 1856 Mendel studied peas which he grew in a garden out side the Abbey he lived in. Showed that the traits he studied behaved in a precise mathematical way and disproved the theory of "blended inheritance.” Mendel’s work was rediscovered in 1900 by three botanists: Carl Correns (Germany) Erich von Tschermak (Austria) Hugo de Vries (Holland) Chromosomes: The Physical Basis of Inheritance:  Chromosomes: The Physical Basis of Inheritance 1866 Mendel published his work 1875 Mitosis was first described 1890s Meiosis was described 1900 Mendel's work was rediscovered 1902 Walter Sutton, Theodore Boveri and others noted parallels between behavior of chromosomes and alleles. Why Peas?:  Why Peas? Mendel used peas to study inheritance because: True breeding commercial strains were availible Peas are easy to grow Peas have many easy to observe traits including: Seed color - Green or yellow Seed shape - Round or wrinkled Pod color - Green or yellow Pod shape - Smooth or constricted Flower color - White or purple Flower position - Axial or terminal Plant size - Tall or dwarf Why Peas?:  Why Peas? Pea flowers are constructed in such a way that they typically self fertilize Because of this, it is relatively easy to control crosses in peas Why Peas?:  Why Peas? Pea flowers are constructed in such a way that they typically self fertilize Because of this, it is relatively easy to control crosses in peas Why Peas?:  Why Peas? By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Why Peas?:  Why Peas? By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Why Peas?:  Why Peas? By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Why Peas?:  Why Peas? By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Why Peas?:  Why Peas? By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Mendel’s Results:  Mendel’s Results When crossing purple flowered peas with white flowered peas, Mendel got the following results: In the first filial (F1) generation all offspring produced purple flowers In the second generation (second filial or F2): 705 purple 224 white Approximately a 3:1 ratio of purple to white Interpreting Mendel’s Results:  Interpreting Mendel’s Results Because the F1 generation did not produce light purple flowers and because white flowers showed up in the F2 generation, Mendel disproved blended inheritance. Mendel said that the parents had two sets of genes thus two copies of the flower color gene Each gene has two varieties called alleles In the case of the flower color gene the two alleles are white and purple Interpreting Mendel’s Results:  Interpreting Mendel’s Results CC Cc Cc cc In the F1 generation, the white allele was hidden by the purple “dominant” allele In the F2 generation, 1/4 of the offspring wound up with two copies of the white allele thus they were white Cc Cc Cc Cc Mendel’s Results:  Mendel’s Results Trait Seeds round/wrinkled yellow/green full/constricted Pods green/yellow axial/terminal Flowers violet/white Stem Tall/dwarf F1 Results All Round All Yellow All Full All Green All Axial All Violet All Tall F2 Results 5,474 Round 1,850 wrinkled 6,022 Yellow 2,001 green 882 Full 299 constricted 428 Green 152 yellow 651 Axial 207 terminal 705 Violet 224 white 787 Tall 277 dwarf Mendel’s Results:  Mendel’s Results F2 Results Seeds 5,474 Round 1,850 wrinkled 6,022 Yellow 2,001 green 882 Full 299 constricted Pods 428 Green 152 yellow 651 Axial 207 terminal Flowers 705 Violet 224 white Stem 787 Tall 277 dwarf F2 Ratios Seeds 2.96:1 Round:wrinkled 3.01:1 Yellow :green 2.95:1 Full:constricted Pods 2.82:1 Green:yellow 3.14:1 Axial:terminal Flowers 3.15:1 Violet:white Stem 2.84:1 Tall:dwarf Ratios are not exactly 3:1 How do we decide if the ratios are close enough to 3:1 to support and not reject our theory? Independent Assortment:  Independent Assortment When Mendel crossed peas and looked at two different traits, he discovered that the traits assorted independently In other words, if he was looking at the height of the plants and the color of the flowers, all four possible combinations of height and flower color were produced: Tall Purple Tall white dwarf Purple dwarf white Independent Assortment:  Independent Assortment As long as genes are on different chromosomes, they will assort independently

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